An adjective describes or modifies a noun.
A big car
A black car
An Italian car
We may have more than one adjective in front of a noun.
A big black Italian car
In English there is a fixed order of adjectives.
3. Physical quality
You would not write *an old nice little lady – a nice little old lady sounds much better (for the use of the asterisk see the comment at the end of this text).
Native English speakers automatically put adjectives in this fixed order, but non-native users of English usually don’t know the rule.
We should remember, of course, that we seldom use a long row of adjectives before a noun – usually only one or two, and then they are often combined with and or but: It was a dark and rainy night. They stayed at a cheap but comfortable hotel.
Why do we say big bad wolf? Bad is an opinion and should come before big (size). But there is another rule that says that vowels follow the order i–a–o. Think of words such as riff-raff, zig-zag, tip-top, flip-flop or hip-hop. Therefore, we say big bad wolf and not *bad big wolf.